The autosomal recessive spinal muscular atrophy (SMA) is one of the most common genetic causes of infant death. In SMA, there is anterior horn cell death and muscle weakness. Deletions or mutations in the survival motor neuron gene, SMN, are responsible for the disease. There are two SMN genes. However, only telomeric copy (SMNt or SMNI) causes disease. Due to a single nucleotide difference, T in the second gene SMN2 from C in SMNI, the majority of SMN2 mRNA or protein skips exon7, resulting in an unstable SMNA7 protein and reduction of its oligomerization ability. Therefore, the presence of the SMN2 gene in SMA patients can not compensate for the loss of the SMNI gene. To understand the pathogenesis of SMA, the first goal of this proposal is to use the yeast two-hybrid screens to identify SMN interacting proteins, particularly those from motor neurons. The interactions will be further characterized by other complementary methods including mammalian two hybrid assays, in vitro binding assays and in vivo co-immunoprecipitation assays. The biological significance of interactions between SMN and its interactors will be investigated in cell lines, and as long-term goals, in animal models. The second goal of this proposal is to develop cell-based systems for therapeutic studies of SMA based on the hypothesis that increasing of total or full-length SMN protein from SMN2 would reduce the severity of SMA. Stable cell lines and transgenic mice expressing exon 7 splicing cassettes with reporters such as GFP, luciferase or P-lactamase will be established. Both high and low throughput screening (HTS, LTS) will be used to identify small molecules to promote inclusion of exon 7 in SMN2 mRNA and protein. These compounds will be tested in SMA mouse models. Signal pathways and other mechanisms that regulate RNA splicing of SMN genes will be investigated. 1 ZNS1 SRB R(01) 3 1 R01 NS41665-01 DECEMBER 13-14, 2000 ZHOU, DR. JIANHUA